Recently, there is an increasing consumer interest in illumination and an illumination apparatus using light emitting diodes (LED elements) as light sources are being diversified. Under these circumstances, there is an increasing number of high-power products and the like in which LED modules, each having multiple LED elements connected in series to each other, are connected in parallel. Further, in order to cope with the wide variability of LEDs, a constant current circuit for supplying a constant current may be provided in the LED modules connected in parallel.
However, in a case where the LED modules are connected in parallel, if some of the LED modules are detached or an open-circuit mode failure occurs therein, there may flow concentrated currents through the other LED modules, and it may lead to destruction and degradation of the LED modules. Even in a case where the current supplied to the entire load is controlled to be constant by using the constant current circuit, the concentrated currents may flow through some of the LED modules. Accordingly, it has been necessary to establish a measure for each LED module.
Thus, there is an illumination apparatus in which a constant current circuit and a connection state detection circuit are provided for each of LED modules connected in parallel (see, e.g., Japanese Patent Application Publication No. 2009-21175). In this illumination apparatus, if it is detected that a certain LED module is detached, the supply of the current to the corresponding LED module is stopped, thereby preventing concentrated currents from flowing through the other LED modules.
Further, there is a lighting circuit which detects an abnormality in an LED load and safely turns on a light source of a vehicle lamp (see, e.g., Japanese Patent Application Publication No. 2004-134147). The lighting circuit supplies a constant current to the entire light source having LED loads connected in parallel. Further, a sense resistor is connected in series to each LED load, and an abnormality such as failure or detachment of an LED load is detected by sensing a voltage across each sense resistor. Further, if an abnormality is detected, the power supplied to the entire LED load is reduced by adjusting a drive signal of a switching regulator, thereby maintaining a safe operation.
However, in the illumination apparatus of Japanese Patent Application Publication No. 2009-21175, since the constant current circuits and the connection state detection circuits need to be provided in the same number as the number of the LED modules connected in parallel, the circuit configuration becomes complicated, and it results in a large power loss due to the constant current circuits and the connection state detection circuits and a low conversion efficiency of the illumination apparatus.
Further, in the illumination apparatus of Japanese Patent Application Publication No. 2004-134147, since the sense resistors need to be provided in the same number as the number of the LED loads connected in parallel, it results in a large power loss due to the sense resistors and a low conversion efficiency of the lighting circuit.